Disclosure of Invention
The invention aims to provide a water distribution method for an ultra-large counter-flow natural ventilation cooling tower, which can improve the uniformity of water distribution of the cooling tower and the reliability of water distribution of the cooling tower.
In order to achieve the purpose, the technical scheme is as follows:
a water distribution method for an ultra-large counter-flow natural draft cooling tower comprises the following steps:
establishing a three-dimensional geometric model of one spray head and establishing a three-dimensional geometric model of a water distribution pipe;
setting a first boundary condition; wherein the first boundary condition comprises: the water flow pressure and the water flow velocity of the water inlet side section of the water distribution pipe, the water flow pressure and the water flow velocity of the spray head, and the water flow pressure and the water flow velocity of the inner pipe wall surface of the water distribution pipe;
acquiring the pressure difference between the water inlet side of the three-dimensional geometric model of the spray head and the spray head side according to the first boundary condition, the preset first water distribution pipe flow, the turbulence energy equation and the turbulence dissipation function equation;
acquiring a water flow resistance coefficient of the spray head according to the pressure difference and the water flow velocity at the spray head;
setting a second boundary condition, wherein the second boundary condition comprises: the water flow pressure measured at the inlet of the water distribution pipe, the pipe wall roughness of the water distribution pipe, the flow area of the spray head and the water flow resistance coefficient of the spray head;
acquiring the water flow of the spray head according to the second boundary condition, the preset second water distribution pipe flow, the turbulence energy equation and the turbulence dissipation function equation;
acquiring the water spraying density of the cooling tower according to the water flow of the spray heads, the number of the spray heads of the cooling tower and the total area of the water spraying area of the cooling tower;
and when the water spraying density of the cooling tower is smaller than the preset water spraying density, the water inflow pressure of the water distribution pipe is increased.
The method comprises the steps of firstly establishing a three-dimensional geometric model of a single spray head and a three-dimensional geometric model of a water distribution pipe, and obtaining the pressure difference between the water inlet side of the three-dimensional geometric model of the spray head and the measured pressure of the spray head by setting a reasonable boundary condition of the three-dimensional geometric model of the spray head and utilizing a preset first water distribution pipe flow, a turbulence kinetic energy equation and a turbulence dissipation function equation; the water flow resistance coefficient of the spray head can be obtained according to the pressure difference; according to the water flow resistance coefficient of the spray heads, the water flow of each spray head is obtained by utilizing the preset second water distribution pipe flow, the turbulence kinetic energy equation and the turbulence dissipation function equation, and the water flow of each spray head can be obtained; according to the number of all spray heads on the water distribution pipe of the cooling tower and the area of a water spraying area, the water spraying density of the cooling tower can be obtained; and when the water spraying density of the cooling tower is smaller than the preset water spraying density, increasing the water inflow pressure of the water distribution pipe. Compared with the traditional water distribution method for the cooling tower, the water distribution method for the cooling tower can improve the uniformity of water distribution of the cooling tower and improve the reliability of water distribution of the cooling tower.
Detailed Description
For the purpose of facilitating an understanding of the present invention, reference will now be made to the following descriptions taken in conjunction with the accompanying drawings.
The invention provides a water distribution method for an ultra-large counter-flow natural draft cooling tower, which refers to a figure 1 and comprises the following steps:
s101, establishing a three-dimensional geometric model of one spray head and establishing a three-dimensional geometric model of a water distribution pipe;
s102, setting a first boundary condition;
setting a first boundary condition; wherein the first boundary condition comprises: the water flow pressure and the water flow velocity of the water inlet side section of the water distribution pipe, the water flow pressure and the water flow velocity of the spray head, and the water flow pressure and the water flow velocity of the inner pipe wall surface of the water distribution pipe.
S103, acquiring a pressure difference between a water inlet side of the three-dimensional geometric model of the spray head and a spray head side according to a first boundary condition, a preset first water distribution pipe flow, a turbulence kinetic energy equation and a turbulence dissipation function equation;
s104, acquiring a water flow resistance coefficient of the spray head according to the pressure difference and the water flow velocity at the spray head;
s105, setting a second boundary condition;
setting a second boundary condition, wherein the second boundary condition comprises: the water flow pressure measured at the inlet of the water distribution pipe, the pipe wall roughness of the water distribution pipe, the flow area of the spray head and the water flow resistance coefficient of the spray head.
S106, acquiring the water flow of the spray head according to a second boundary condition, a preset second water distribution pipe flow, a turbulence kinetic energy equation and a turbulence dissipation function equation;
s107, acquiring the water spraying density of the cooling tower according to the water flow of the spray heads, the number of the spray heads of the cooling tower and the total area of the water spraying area of the cooling tower;
and S108, when the water spraying density of the cooling tower is smaller than the preset water spraying density, increasing the water inflow measuring flow pressure of the water distribution pipe.
For a better understanding, the detailed description will proceed from the following steps, including:
firstly, establishing a three-dimensional geometric model of one spray head and establishing a three-dimensional geometric model of a water distribution pipe;
when a three-dimensional geometric model of one of the nozzles is established, the following method can be adopted: acquiring the diameter D1 of a nozzle of the spray head and the diameter D2 of a water distribution pipeline, wherein the length of the water distribution pipeline is 15 times of the diameter of the water distribution pipeline, the inlet end (water inlet side) is 10 times of the diameter of the pipeline, the other end of the water distribution pipeline is 5 times of the diameter of the pipeline, and the tail end of the pipeline is in a wall surface condition, so that a three-dimensional geometric model of the spray head is established;
when the three-dimensional geometric model of the water distribution pipe is established, as the pipelines are strictly symmetrical, in order to avoid excessive calculation amount, the model is established for half of the water distribution pipe.
Secondly, setting a first boundary condition;
when boundary conditions are set, dense grids are divided at the joint of the water distribution pipeline and the spray head, the size of the initial grid at the wall surface is 1mm, the growth rate is 1.1, and the size of the maximum grid is 6 mm. Because the water distribution pipeline is very long, a small area is selected for grid division of the part, two sections of the water distribution pipeline are selected at positions 100mm away from the two sides of the central axis of the spray head pipeline respectively to form a part of area body, and the total number of the part of grids is 42 ten thousand.
The nozzle part of the nozzle is processed in the same way as a water distribution pipeline in a grid mode, the cross section is subjected to grid encryption, the number of grids on the side wall surface is given, the grid division is finished by stretching and tiling, the initial size of the grid on the cross section is 0.5mm, the growth rate is 1.08, the maximum grid is 3mm, and the total number of the grids is 4.3 ten thousand;
setting a first boundary condition according to the grid.
Acquiring the pressure difference between the water inlet side of the three-dimensional geometric model of the spray head and the spray head side according to the first boundary condition, the preset first water distribution pipe flow, the turbulence energy equation and the turbulence dissipation function equation;
specifically, the turbulence energy equation (k-equation):
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wherein,μt=ρCμk2/ε,μk=μ+μt/σk,με=μ+μt/σε
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Cμ=0.09,σk=1.0,σε=1.3,C1=1.44,C2=1.92,ρ,k,ε,μ,μtfluid density, turbulent kinetic energy, turbulent dissipation ratio, hydrodynamic viscosity coefficient and turbulent viscosity coefficient; u and v are the components of the fluid velocity in the directions x and r respectively; x-direction (vertical direction) r-direction (radial direction).
The specific calculation is carried out on FLUENT software.
And acquiring the pressure difference delta P between the water inlet side of the three-dimensional geometric model of the spray head and the spray head side through the first boundary condition, the preset first water distribution pipe flow, the turbulence energy equation and the turbulence dissipation function equation.
Fourthly, acquiring a water flow resistance coefficient of the spray head according to the pressure difference and the water flow velocity at the spray head;
in particular, according to the formulaAcquiring a water flow resistance coefficient of the spray head;
wherein Δ P is a pressure difference; xi is the water flow resistance coefficient of the spray head; ρ is the density of water; v is the water flow velocity at the spray head.
In order to improve the accuracy, a plurality of preset first water distribution pipe flow rates can be input, so a plurality of pressure differences can be obtained according to the third step;
according to the pressure differences in the third step, the water flow resistance coefficients of the plurality of spray heads can be obtained in the step;
and calculating the average value of the water flow resistance coefficients of the plurality of spray heads. And setting the water flow resistance coefficient of the spray head in the fifth step by using the average value of the water flow resistance coefficients of the spray head.
Fifthly, setting a second boundary condition;
specifically, when a second boundary condition is set, the whole water distribution pipeline is divided into grids, the grids close to the wall surface are encrypted, the size of the initial grid of the coarse pipeline from the wall surface to the center of the pipeline is 6mm, the maximum grid is 20mm, and the grid growth rate is 1.2; the initial grid of the thin pipeline from the wall surface to the center of the pipeline is 4mm, the maximum grid is 15mm, and the grid growth rate is 1.1.
The mesh division at the joint of the water distribution pipeline and the spray head is dense, two sections of the water distribution pipeline are selected at positions which are 50mm away from the central axis of the spray head at two sides respectively to form a small area for carrying out the mesh division of small bodies at the spray head, the mesh size is gradually increased by diffusing outwards from the spray head, the initial mesh size is 1mm, the growth rate is 1.1, and the maximum mesh size is 6mm at the spray head with a thick pipe diameter; at the nozzle with the thin pipe diameter, the initial grid size is 1mm, the growth rate is 1.1, and the maximum grid size is 4 mm.
The mesh division is also denser at the different-pipe-diameter joint, the mesh size gradually increases from one end with a thin pipe diameter to one end with a thick pipe diameter, the initial mesh is 4mm, the growth rate is 1.15, and the maximum mesh size is 6 mm.
And setting a second boundary condition according to the water distribution pipe grid.
In addition, the cooling tower of the power station is generally in an unattended state during the annual operation, and under the long-time operation condition, the actual examination of the cooling tower with a groove-type water distribution system shows that the phenomena of deposition and partial blockage of the water distribution pipe and the nozzle exist, and the growth of marine organisms can also occur when seawater is used as a circulating medium, so when the second boundary condition of the old water distribution pipe is set, the pipe wall roughness of the water distribution pipe and the overflowing area of the spray head are properly adjusted.
Sixthly, acquiring the water flow of the spray head according to a second boundary condition, a preset second water distribution pipe flow, a turbulence kinetic energy equation and a turbulence dissipation function equation;
seventhly, acquiring the water spraying density of the cooling tower according to the water flow of the spray heads, the number of the spray heads of the cooling tower and the total area of the water spraying area of the cooling tower;
because the spray heads on the water distribution pipes of the cooling tower are uniformly arranged and the specifications of the spray heads are almost consistent, the water spraying density of the cooling tower can be obtained according to the water flow of one spray head, the number of all spray heads on the water distribution pipe and the total area of the water spraying area of the cooling tower.
And eighthly, when the water spraying density of the cooling tower is smaller than the preset water spraying density, increasing the water inflow pressure of the water distribution pipe.
And when the water spraying density of the cooling tower is smaller than the preset water spraying density, increasing the water inflow pressure of the water distribution pipe.
In one embodiment, in order to facilitate the staff to master the water distribution condition of the cooling tower, the method further comprises the following steps: and sending an alarm prompt.
The method comprises the steps of firstly establishing a three-dimensional geometric model of a single spray head and a three-dimensional geometric model of a water distribution pipe, and obtaining the pressure difference between the water inlet side of the three-dimensional geometric model of the spray head and the measured pressure of the spray head by setting a reasonable boundary condition of the three-dimensional geometric model of the spray head and utilizing a preset first water distribution pipe flow, a turbulence kinetic energy equation and a turbulence dissipation function equation; the water flow resistance coefficient of the spray head can be obtained according to the pressure difference; according to the water flow resistance coefficient of the spray heads, the water flow of each spray head is obtained by utilizing the preset second water distribution pipe flow, the turbulence kinetic energy equation and the turbulence dissipation function equation, and the water flow of each spray head can be obtained; according to the number of all spray heads on the water distribution pipe of the cooling tower and the area of a water spraying area, the water spraying density of the cooling tower can be obtained; and when the water spraying density of the cooling tower is smaller than the preset water spraying density, increasing the water inflow pressure of the water distribution pipe. Compared with the traditional water distribution method for the cooling tower, the water distribution method for the cooling tower can improve the uniformity of water distribution of the cooling tower and improve the reliability of water distribution of the cooling tower.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.